A few simple rules are expected to attract more than 50,000 participants to today's 12th annual Dyke March through San Francisco: no corporate sponsors, no politicians, no permit to march and no men. Dyke- friendly guys are invited to cheer from the sidewalk as marchers wind along a still-secret route through the Mission and Castro districts and points beyond.

Organizers promise the performance stage this year will be dude-free as well, a rule that's been broken in the past by the stray male backup singer or other dollop of testosterone. Another new, perhaps only-in-San Francisco wrinkle: In a nod to the evolving gender spectrum, marchers are welcoming not only dykes but those who "are questioning and challenging gender constructs imposed by the mainstream and do not necessarily identify as women."

Or, of course, as men.

It's cutting-edge politics like this that has helped the march blossom as a centerpiece of pride weekend, to which it is not officially related nor wants to be.

While Sunday's gay pride parade is fueled by corporate donations from the likes of Budweiser, Delta Air Lines and The Chronicle, and is a magnet for grinning politicos strolling up Market Street, the Dyke March has remained true to its grassroots origins, participants and organizers say.

The event is put on by an all-volunteer staff working with this year's record budget of $20,000, most of which has been blown on the sound system. The biggest donation was a $5,000 gift from the city's Grants for the Arts. Organizers are banking on a lot of T-shirt sales.

The reason for maintaining a female-only environment is simple, said organizer Fresh! White (exclamation intended): "There are no other spaces where we can do that. There is a statement to be made that women can stand up and do it alone."

The same goes for calling it a "dyke" and not a "lesbian" march. Organizer Tina D'Elia said it's an effort to reclaim the word "dyke," long considered a derogatory term for lesbians. She said that kind of self- empowerment has fostered a safe space where the more brazen participants have felt comfortable enough to march topless and where the majority has been happy just to swim in what artist Kris Kovick called "three hours of monolithic lesbian unity."

While San Francisco's version has become the largest of the 20-odd Dyke Marches nationally, the first was held in Washington, D.C., in 1993. It was created by a dozen San Francisco women over dinner one night in the Mission District.

They were about to leave for a huge gay-rights march in Washington, recalled co-founder Lisa Roth, "and we were dreading it. We were like, 'Oh, God, just another male-dominated queer event. How boring.' "

Still, they had to go, even if they felt "marginalized." As Roth, a veteran of the peace movement, knew, street numbers mean everything when the public gauges the strength of a movement, gay or straight. But the women came up with an idea for something to do the night before the Washington event: A dyke-only march through Washington. If they got 1,000 people, Roth recalled, they'd be happy.

They spread the word through local chapters of ACT UP and other activists groups. Armed with a single bullhorn, the first Dyke March drew 20,000 people on a meandering stroll around Washington that ended with an impromptu rally underneath the Washington Monument, or, as Roth said it was dubbed for the evening, "the big (phallus)."

"Obviously we touched a need in the community," Roth said. A few months later, they pulled together San Francisco's first Dyke March, attended by 5, 000 participants.

Since then, it's become one of the city's largest winked-at underground events. Though there are no official march permits, the city's police, traffic and transportation officials now plan for it. And while a microphone on a flat- bed truck held the entertainment offerings those first few years, the 2004 version will have 17 entertainers, ranging from speakers to singers to drag kings.

Yet the soul of the Dyke March has been rooted in progressive, some might say radical, politics. While Sunday's pride parade has at times shied away from politics -- it didn't take a stand on a 2000 California ballot initiative that banned gay marriage and approved an anti-war resolution last year only after some consternation -- the Dyke Marchers have thrived on it.

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This year's theme is "Uprooting Racism," and while the rest of the gay world may be celebrating the gains of the last year, some Dyke Marchers aren't as giddy. Not with conservatives -- including President Bush -- pushing a constitutional amendment banning gay marriage.

"It's insane," said Roth, a veteran of the 1969 Stonewall riots in New York that spawned the modern gay rights movement.

"Young women feel oppression every day," said organizer Mo Kalman, an attorney in the Castro. "When people say, 'When you get married' or 'When your husband blah-blah-blah' to a young woman, there's a lot of assumptions made. People are put on the same track from the time they're children, no matter what."

This year, Roth is going to sit back and fully enjoy the event; she's taking a sabbatical from the march she helped to co-found. A new, more diverse group of organizers -- a third are women of color, and the age range now spans 40 years -- has picked up the torch. The new crew has diversified the entertainment and has brought in ideas such as a motorized cable car to ferry older and disabled marchers along the route.

Recently, Roth saw a small exhibit on the history of the Dyke March that's on display at the San Francisco Main Library. A video in the exhibit showed women from small towns telling how powerful it was to march surrounded by tens of thousands of lesbians.

Todays celebration begins at noon in Civic Center Plaza and runs until 6p.m. On Sunday, it begins at noon and runs until 7 p.m. The parade is onSunday and begins at 10:30 a.m., traveling west along Market Street toEighth Street.

Muni: Extra service will be provided in the Metro subway between the West Portal andEmbarcadero stations from 8 a.m. to about 8 p.m. on Sunday. Several bus lines in the downtown area will be rerouted. For more information, contact: www.sfmuni.com.

Golden Gate Transit: Sunday from 10 a.m. through 4 p.m. Golden Gate Transit bus stopssouth of Broadway and Van Ness Avenue will not be served. From 7 p.m. today through Sunday, at 4 p.m., Golden Gate Transit bus stops in the San Francisco Civic Center area will not be served. For more information, contact: www.goldengate.org SamTrans: Regular Sunday schedule..

AC Transit: Regular Sunday schedule.

BART: Disembark at Civic Center for the celebration site. Use the Civic Center, Powell and Montgomery Street stations to access the parade route. BART will provide longer trains. Trains will operate on a regular Sunday schedule at 20-minute intervals on three lines: Richmond/Fremont, Pittsburg/Bay Point- SFO and Dublin/Pleasanton-Daly City..

Caltrain: If you are coming from the Peninsula or Santa Clara County, take the train to the end of the line at Fourth Street. The parade route is a seven-block walk away. The celebration site is a short Muni ride away. Contact Caltrain at (800) 660-4287 for latest information and schedules. The first three scheduled trains on Sunday arrive in San Francisco at 8:36 a.m., 9:36 a. m. and 10:36 a.m. Trains will stop at all stops. The lastsouthbound train leaves San Francisco at 9 p.m. For more information, contact: www.caltrain.org